There is a widespread need for inspection data for electronic parts in a manufacturing environment. Machine-vision systems have become vital to many complex manufacturing processes, particularly for quality control. For example, during the manufacture of integrated circuits which contain millions of transistors and other electrical components, machine-vision systems visually inspect the circuits at various manufacturing stages for surface blemishes or other defects, rejecting or accepting circuits based on appearance.
Machine-vision systems typically includes an imaging device, such as an electronic camera and an illumination system, which illuminates an object for the camera. The typical illumination system, generally designed to illuminate all sides of an object simultaneously, comprises some form of a circular ring of lights, for example a ring-shaped flashtube, a ring of light-emitting diodes, or a ring of optical fibers. The circular ring of lights usually lies between the camera and object, with the camera looking down through the ring to the object and the lights oriented down and inward to the object.
Conventional illumination systems suffer from at least two major problems. First, they lack a convenient way for varying the angle of illumination, that is, the angle light strikes an object. Conventional illumination systems require technicians to manually adjust orientation of the complete ring of lights or to manually adjust orientation of its individual lights. However, manual adjustments are not only time consuming, but often lead to angular variations which compromise consistency of machine-vision systems. Second, conventional systems lack convenient way of switching from one illumination mode to another, for example, from a particular selected angle of illumination to a multi-directional object illumination, such as “cloudy-day illumination.” Some select-angle illumination modes are better for viewing scratches, while cloudy-day illumination is better for specular or irregular surfaces. This lack of a convenient way of switching illumination modes often leads to use of more than one machine-vision system, and thus forces manufacturers to buy separate systems, to use human inspectors, or to skip inspection for some types of defects. Accordingly, there is a need for better illumination systems for machine-vision systems.